Three second-half tries were enough to get Australia home as their Sydney Sevens defence began with a 19-0 win against Spain on Friday.
But, after a scoreless first half against the European minnows at Spotless Stadium, they know they must improve to repeat their efforts of 12 months earlier.
The hosts were well roped in by Spain’s valiant cover defence in the first half, unable to break the line in a rare seven-minute stalemate.
A half-time huddle did the trick though, as Ellia Green broke the deadlock within a minute of the restart.
Emma Sykes then broke the line for a try of her own, before another probing run from Green ended in an Evania Pelite five-pointer.
Sykes admitted there had been plenty of cobwebs, but that Spain deserved credit for keeping them at bay for so long.
“They’re a very physical team; I know when we play them that we’ve got to be up physically,” Sykes said.
“Every time you play them they’re improving; you can’t go into a world series underestimating any team.
“It was a good win in the end, good to keep them to nil.”
Series leaders New Zealand won their opener against Papua New Guinea 38-5, while France beat England 27-14 and Canada toppled Fiji 36-12.
The United States, who sit one place above Australia on the series standings in third, beat China 26-10 in their opening match.
Australia play both those sides in their final pool games later on Friday.
Australia’s men, who are sixth after three world series legs, play pool games against Argentina, Tonga and South Africa on Saturday.